To determine the moving speed and direction by generating different signals with three phases in correspondence with the signal from a transponder, detecting the changing patterns of the respective signals, storing them and comparing the current patterns with the stored ones.

A reader generates signals 60, 62 and 64 in correspondence with the signal receiving from a transponder, and they depend on the relative phase of antenna signal and reference signal. Exclusive OR gates 70, 72 and 73 input the signals 60 and 63, 62 and 64 and 60 and 62 respectively to generate signals 71, 73 and 75. An FF in a logical element stores the state change information of the signals 71, 73 and 75 and compares them with stored ones so as to judge whether the transponder becomes closer or farther to/away the reader, then it gives the removing direction by turning on/off an LED 98. In addition, the relative removing speed of the transponder is obtained by turning on/off the LED 96 by the frequency of the signal state change of either one of the signals 71, 72 and 73 and obtaining the moving speed directly proportional thereto.